if they are working correctly you shouldn't get any water in the tanks. Actually it doesn't make any sense all. Even if for some reason the gates got stuck open(all or part way) they would empty when you get on plane. There isn't actually a way for the tanks to fill and stay full unless you are opening them and then closing before taking off.

I have checked the functionality of both gates and they appear to be working properly. The tanks will empty while open and underway.

I was out for about 3.5 hours on Saturday and never opened the gates. I have my wife open the gates when we load up, just to make sure everything is empty and I would say they were more than half full. Both tanks emptied about the same amount which tells me they are leaking at the same rate.

I have a Epic and I noticed that my gates have a orange gasket on them. Mine work fine but if the gaskets were torn or gone I could see it leaking. Not sure how yours works but if you have gaskets I would start there.

I'd call drainmaster. They are very helpful. What you are experiencing is not normal. If it were, we'd see RVs driving down the highway all the time leaking their black water tanks (the other implementation of these valves).